Quantitative assessment of normal adrenal gland metabolic activity using time-of-flight (TOF) with resolution recovery versus non-TOF PET reconstructions

1986 Objectives TOF reconstruction with resolution recovery (TOF-RR) could increase the observed activity in normal adrenal glands without associated pathology over non-TOF reconstruction. This is important as newer PET-CTs are equipped with TOF-RR. This study serves to quantify physiologic activity in normal adrenal glands using different reconstructions to prove increased baseline activity on TOF-RR PET-CT relative to non-TOF PET-CT. Methods Data from 49 consecutive patients who underwent PET-CT were evaluated. Patients were excluded if there was any evidence of adrenal gland disease on CT or other available imaging modalities. TOF-RR, TOF without resolution recovery (TOF only), and non-TOF were reconstructed with OSEM of 3 iterations and 24 subsets. Regions of interest were contoured around the right and left adrenal glands on fused PET-CT images using proprietary software. SUVmax was recorded for each adrenal gland, and comparative statistical analysis was performed. Results Paired t-tests were used to determine if there was a difference between the adrenal gland SUVmax on TOF-RR vs. non-TOF reconstructions. For the left adrenal gland, the mean difference (M=0.1353, SD=0.3791) was statistically significant, t=2.4982, two tail p=0.016. For the right adrenal gland, the mean difference (M=-0.0149, SD=0.3797) was not statistically significant, t=-0.2747, two tail p=0.7847. Additionally, paired t-tests were used to determine if there was a difference between the adrenal gland SUVmax on TOF only vs. non-TOF reconstructions. For both the left and right adrenal glands, the mean difference (M=0.0692, SD=0.3622 and M=0.0106, SD=0.3512, respectively) was not statistically significant (left: t=1.13371, two tail p=0.1875; right: t=0.2115, two tail p=0.8334). Conclusions There is a statistically significant difference in SUVmax for the left adrenal gland between TOF-RR and non-TOF, with increased SUVmax on TOF-RR. This is in keeping with the hypothesis of perceived increased baseline adrenal activity. There is not a statistically significant difference for the right adrenal gland SUVmax between TOF-RR and non-TOF reconstructions. The authors hypothesize that this is likely due to the right adrenal gland’s close proximity to the liver with spurious liver activity making an accurate quantification of activity difficult; hence, the left adrenal gland appears to be a better surrogate to answer this question. Furthermore, there is not a statistically significant difference between TOF only and non-TOF reconstructions, which suggests that the perceived increased activity is primarily due to resolution recovery.